From Wikipedia, the free encyclopedia
The order Cetacea
includes the whales
and comprise the mammals most fully adapted to aquatic life. It contains 81 known species organized in two suborders: Mysticeti
(baleen whales) and Odontoceti
(toothed whales, which includes dolphins and porpoises). The order contains several record breaking species, with the Blue Whale
being the largest animal known, and the Orca
being the most widely distributed animal.
Cetaceans evolved from land mammals that adapted to marine life about 50 million years ago. Over a period of a few millions of years during the Eocene, the cetaceans returned to the sea. Their body is fusiform (spindle-shaped), the forelimbs are modified into flippers, the tiny hindlimbs are vestigial and the tail has horizontal flukes. Cetaceans are nearly hairless, and are insulated by a thick layer of blubber.
Cetaceans inhabit all of the world's oceans, as well as some rivers in South America and Asia. Some species can be found across the globe.
Cetology is the branch of marine science associated with the study of cetaceans.
The Sei Whale (Balaenoptera borealis) is a baleen whale, the third largest rorqual after the Blue Whale and the Fin Whale. It can be found worldwide in all oceans and adjoining seas, and prefers deep off-shore waters. It tends to avoid polar and tropical waters and semi-enclosed bodies of water. The Sei Whale migrates annually from cool and subpolar waters in summer to temperate and subtropical waters for winter, although in most areas the exact migration routes are not well known.
The whales reach lengths of up to 20 metres (66 ft) long and weigh up to 45 tonnes (50 tons). It consumes an average of 900 kilograms (2,000 lb) of food each day, primarily copepods and krill, and other zooplankton. It is among the fastest of all cetaceans, and can reach speeds of up to 50 kilometres per hour (31 mph) over short distances.
Following large-scale commercial hunting of the species between the late-nineteenth and late-twentieth centuries when over 238,000 individuals were taken, the Sei Whale is now an internationally protected species, although limited hunting still occurs under controversial research programmes conducted by Iceland and Japan. As of 2006, the worldwide population of the Sei Whale was about 54,000, about a fifth of its pre-whaling population.
More on the Sei Whale
- ...dolphins often leap clear of the water when travelling at speed. This is because the density of water is much greater than that of air and they are able to travel faster by leaping out of the water.
- ...whale and dolphin mothers ‘suckle’ their young underwater! Mothers have muscular mammary glands and ‘squirt’ their milk into the calf’s mouth, to ensure that the calf takes in as much of the energy rich milk as possible.
- ...on average, a whale or dolphin will eat four to five percent of its body weight in food per day. That means that a 100 ton blue whale will eat almost five tons of krill per day, or that a 200kg bottlenose dolphin will eat 10kg of fish per day!
- ...newborn cetacean calves ‘suckle’ three to four times each hour and will suckle from their mothers for six months or more.
Here are some Cetaceans WikiProject tasks you can do.
- Patrol: Look through the Category:Cetaceans for recent changes
- Assessment: Unassessed cetacea articles and unknown-importance cetacea articles.
- Copyedit/Formatting: Bottlenose dolphin, Beached whale
- Expand: Hector's beaked whale, Ginkgo-toothed beaked whale, Shepherd's beaked whale, Archaeoceti, Cumberland Sound beluga, Blubber, Baiji, Humpback dolphin, Amazon river dolphin
- Stubs: Bolivian river dolphin (new species), Cephalorhynchus
- Images: Pictures of the baiji are wanted.
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See also Wikispecies, a Wikimedia project dedicated to the classification of species.